Returning an arrow function from a function

Question | Jul 3, 2019 | hkumar 

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The SphereVolumeFormula function returns an arrow function that computes and returns volume of a sphere of a specific radius r:

function SphereVolumeFormula(r) {
  // returning an arrow function 
  return () => (4/3)*Math.PI*(r*r*r);

// Get a volume formula function for a sphere of radius 2
let formula = SphereVolumeFormula(2);

What is the result of calling formula() ?